Method of making an electrical connection



Nov. 28, 1961 E. W. FORNEY, JR

METHOD OF MAKING AN ELECTRICAL CONNECTION Filed Nov. 13, 1958 2Sheets-Sheet 1 INVENTOR. Edgar w. Fomeq, dr.

Nov. 28, 1961 w. FORNEY, JR 3,010,184

METHOD OF MAKING AN ELECTRICAL CONNECTION Filed Nov. 13, 1958 2Sheets-Sheet 2 t; 5 an 6 w E] INVENTOR.

EDGRR W. Foauenfik 16 2 6 film/u; m/W

United States Patent 3,010,184 METHOD OF MAKING AN ELECTRICAL CONNECTIONEdgar W. Forney, Jr., Harrisburg, Pa., assignor t0 AMP Incorporated,Harrisburg, Pa. Filed Nov. 13, 1958, Ser. No. 773,638

' 2 Claims. (Cl. 29-15555) This application is a continuation in part ofmy copending application Serial No. 623,956, filed November 23, 1956,for Crimping Connection and Method.

This invention relates particularly to electrical connectors andconnections although it has utility in other environments. It is anobject of the invention to provide a substantially moistureproof andfluid impervious electrical connection between a ferrule and aconductor. A further object is to provide an improved seal between aconductor and a sheath extending thereover. A still further object ofthe invention is to provide a method of reducing the diameterof asubstantially cylindrical ferrule of circular cross section while theferrule is positioned on a cylindrical member thereby to reformthe'ferrule in such a manner that it is, after reforming, inconstrictive embracing relationship with the cylindrical member.

These and other objects of the invention are achieved in a preferredembodiment in which the ferrule is positioned in surroundingrelationship to the conductor and it is then forced into a female diehaving a width less than the diameter of the ferrule so that the ferruleis flattened and the conductor is pinched between the sides thereof.Thereafter, and while the ferrule is contained within the die, it iscompressed along its long axis until it is again formed into asubstantially right circular cylinder of a diameter less than itsinitial diameter. At the conclusion of this operation, the ferrule is inconstrictive embracing relationship to the conductor around its entireperiphery. The invention has utility in forming substantiallyfluid-impervious seals between a conductor and a sheath of elastomericmaterial arranged concentrically with respect thereto. Thus, if the endsof two wires are spliced in any manner, a sheath can be placed aroundthe splice and the sheath sealed to the conductors at each end thereof,whereby the electrical connection between the wire ends is substantiallyhermetically sealed and is suited for usage in corrosive environmentsThe invention also has utility in the formation of certain electricalconnections between wires and ferrules and particularly solid wiressince the initially circular ferrule can be reduced in its diameter intoconstrictive embracing relationship with the wire in a manner whichensures a permanent and highly conductive electrical joinder of theparts and, in addition, a mechanical connection having a high degree ofmechanical strength and resistance to deleterious effects such as vibration and corrosion.

In the drawings: FIGURE 1 is a side view partly in section of one for ofsplice connector for two wires in accordance with the invention; i I

FIGURE 2 is a view similar to FIGURE 1 but showing the parts after theconnector has becn'crimped and the sealing ring constricted;

' FIGURE 2A is a view taken along the lines 2-2 of native embodiment ofthe invention before and after FIGURE 10 is an enlarged sectional viewwith parts broken away of a bushing which forms part of the embodimentof FIGURES 8 and 9; and

FIGURE 11 is a perspective view of an electrical connection between asolid Wire and a terminal in accordance with the invention.

Referring now to FIGURES l and 2, in a preferred embodiment, there isprovided a wire connector ferrule 2 which receives the stripped ends 4of a pair of conductors 5 which are to be connected. Wire ferrule 2 maybe, for example, of the type shown in the United States patent to BroskeNo. 2,478,082 and is provided with a plastic sleeve or sheath 6 whichextends axially for a substantial distance beyond its ends. Sleeve orsheath 6 has a frusto-conical transition section 8 beyond the ends offerrule 2 and beyond this transition section there is provided ashoulder 10 against which is positioned a cylindrical ferrule 11. Abushing or adaptor 12 is fitted within the open end of sleeve 6 and iscentrally apertured for reception of conductor 5. Advantageously, asshown in FIGURE 1, this aperture in bushing 12 tapers towards ferrule 2so that the insulated conductor can be partially inserted into thebushing while the exposed strands 4 extend through the narrow open endof the bushing and into the ferrule 2.

In use, a suitable crimping tool is employed to crimp ferrule 2 onto thewire ends as is commonly known to the art and as is described in theaforementioned Broske Patent No. 2,478,082. The crimped sections shownat 13 in FIGURE 2 establish the electrical connection between the twoconductors 5.

In order to establish a substantially fluid-impervious seal at the endof the sheath 6, the ferrule 11 is reduced in diameter, or constricted,until it is in constrictive embracing relationship with the sleeve orsheath 6, the bushing 12, and with the insulation 5 of the wire. It willbe apparent from FIGURE 2 that after such constriction of the ferrule,the ferrule is longitudinally extruded somewhat and the bushing and theinsulating sheath are compressed radially inwardly against theinsulation 5. Since the bushing is compressed substantially uniformlyaround its entire periphery, there are substantially no irregularitiesin the circular section shown such as would form small passages whichwould admit fluids.

Turning now to FIGURES 3-6, the ferrule 11 is constricted by means of adie set comprising a female die 14 and a male die 16. These dies may bemounted on a suitable press or on a hand tool for relative motiontowards and away from each other. Female die 14 has a recess havingparallel sides 18 which merge with a semicylindrical portion 19. Thewidth W of this recess will in all instances be less than the diameterof the ferrule 11 as indicated in FIGURE 3 the radius R of semicircularportion 19 is equal to the radiuszdesired in the constricted ferrule.cess is rounded as shown at 21 to facilitate entry of the ferrule asshown in FIGURE 4. Die 16 has a concave upper surface 20 which is ofsubstantially the same radius, R as the base of the recess 18. The widthof die 16 should closely approach the width of W of the recess in thefemale die for reasons which will be explained below.

1 In practice, the ferrule 11 is positioned as shown in FIGURE 3 and theram or tool on which the dies are mounted is actuated to drive the maledie relatively towards the female die. As shown in "FIGURE 4, ferrule 11is initially forced into the recess in the female die and the ferrule isreformed at this time until it has a substantially oval-shapedcross-section asbest shown in FIGURE 5. During the stepillustrated atFIGURES 4 and 5, the bushing 11 is compressed from opposite sides and,depending upon'its elastic properties, may be longitudinally or axiallyextruded somewhat.

Advantageously, the mouth of this re-.

After the ferrule 11 has been formed as shown in FIG- URE 5, the diesare further driven towards each other to compress the ferrule and toagain form it into a right circular cylinder having a substantiallycircular crosssection as shown in FIGURE 6. During this final step,bushing 12 is further compressed and longitudinally extruded and ferrule11 is also longitudinally or axially extruded to some extent. The sheath6 is also compressed and extruded beneath ferrule 11. The finished sealand connection can then be removed from the dies and the ferrule willretain its shape substantially as shown in FIGURE 6. The seal producedby this method is substantially moisture proof by reason of the factthat the bushing 12 and the sheath 6 are uniformly compressed aroundtheir entire peripheries onto the insulation 5 of the conductor. Many ofthe prior art moisture proof seals of this type attempted to achieve ahigh degree of moisture resistance by flattening the ferrule. Ingeneral, many of these attempts were not fully successful by reason ofthe fact that abrupt bends were formed in the cross section of thefinished seal and passages eventually opened up at these bends whichadmitted fluids.

For best results several precautions should be followed in practicingthe invention as follows. The bushing 12 should be of a relatively hardbut elastic material such as neoprene and the ferrule 11 should be ofrelatively soft copper or other highly ductile metal. It will beapparent from an examination of FIGURES 3-6 that the sides of theferrule-as shown in FIGURE 5 are restrained from collapsing inwardlytowards each other by the bushing 12, therefore, if this bushing is ofan extremely soft material, it may not present sufiicient resistance tothe ferrule and such collapsing may take place. On the other hand, ifthis bushing is of relatively hard material, it will prevent inwardcollapse of the ferrule so that the ferrule will extrude longitudinallyrather than collapse. In effect, the bushing (or the wire in alternativeembodiments described below) functions as a resilient mandrel over whichthe ferrule is extruded during the constricting operation. After theferrule has been constricted, the bushing tends to return to itsoriginal shape but is prevented from doing so by the constrictive effectof the ferrule. Thus, the bushing stores energy elastically and itssurfaces are continuously urged outwardly against the sheath 6 andinwardly against the wire and its insulation to establish the desiredmoisture-proof seal. The ferrule 11 should be of a relatively soft andductile metal such as soft copper although metal somewhat harder thansoft copper may be used if desired or necessary in order to permitassembly of the ferrules to the sheaths. In any event, it is apparentthat a balance of properties of the ferrule and the bushing must bemaintained for success. The bushing must be sufficiently hard to preventinward collapse of the ferrule but should not be overly stiff or hardsince the harder this member is, the more energy required to perform theconstricting operation. The ferrules should be relatively soft so thatit will flow axially upon crimping rather than collapse inwardly asexplained above.

It will be noted from FIGURE 7 that the die 14 is of a length which isgreater than the length of the ferrule ll after constriction thereofabout the bushing and it will be noted from FIGURE 5 that the depth ofthe recess 18 is sufficient to accommodate the entire cross-section ofthe ferrule after it has been ovalled. The ferrule is thus confinedaround its entire periphery and through its entire length during allstages of the constricting operation. This arrangement is advisable forbest results 'since it ensures that the ferrule will be axially extrudedduring the constricting operation and the pressures developed during theoperation will not be relieved.

It has been found in practice that the diameter of the ferrule mayadvantageously be reduced by 20% to 30% where the bushing is of neopreneand the ferrule is of soft copper. These limits are not critical,however, and greater or lesser reduction might be found to give goodresults depending upon the physical properties of the parts and theirdimensions. For example, where the copper ferrule is initially in a workhardened condition it can not be extruded by the same amount as a softcopper ferrule and the optimum degree of constriction might be less than20%. Under such circumstances it would be desirable to have the wire fitrelatively snugly within aperture in the plug in order that the sealwill be substantially impermeable even though the degree of constrictionis relatively low. It might be found to be practicable to reduce theferrule diameter by an amount greater than 30%, particularly if theaperture in the bushing is relatively large with respect to the wirediameter, since the bushing must tightly embrace the wire to ensure agood seal.

The ferrule should be relatively thin walled in order that it might beextruded without the exertion of an unduly high force, but should, ofcourse be adequate for purposes of strength. For example, where the plugis of neoprene having a hardness of about Durometer A7D and having adiameter of 0.375 inch, good results are obtained if the ferrule has awall thickness of 0.015 inch and a length of 0.280 inch. Where the partsare of these sizes, the ferrule can be constricted by means of a forcemultiplying hand tool. It has been found that the ferrule is extruded bya somewhat greater amount in those sections which are in contact withthe female die so that the finished constricted ferrule is somewhatlonger at its top, as shown in FIGURE 7, than at its bottom. Thiscondition does not, however, detract from the effectiveness of the seal.

As mentioned above, the width of the male die should be almost equal tothe width W of the recess of the female die. As a practical matter, thewidth of the male die must be slightly less than W in order to permitentry of the die into the recess. As a result of the fact that the fitis less than perfect, a small amount of the metal of the ferrule may beextruded downwardly, as viewed in FIGURE 5, between the recess and thesides of the die and die marks 13 may appear on external surface of theconstricted ferrule. These die marks do not detract from theeffectiveness of the seal since the cross sectional configuration of theparts is substantially circular and their arrangement is substantiallyconcentric. Of course, the benefits of the invention will be at leastpartially lost if the width of the male die is grossly less than thewidth W of the recess since, under such circumstances, the metal willmerely extrude downwardly as viewed in FIGURE 5 and the internaldiameter of the ferrule will not be reduced sufficiently to compress theplug and establish the seal.

Referring now to FIGURES 8 and 9, in an alternative embodiment of theinvention a plurality of wires 5 can be connected together at a commonpoint by the use of bushing 12' having a plurality of openings therein.It will be noted in FIGURE 10 that the bushing has the openingssubstantially symmetrically arranged so that the pressure developedduring the constricting operation is evenly distributed. It is alsodesirable in this embodiment to gather the strands of the conductor andsecure them together by means of a relatively small ferrule 22 to ensuretheir entry into the connector or wire ferrule 2.

FIGURE 11 shows an embodiment in which a constricted tubular ferrule 28of a terminal 26 establishes the electrical and mechanical connectionbetween this terminal and a solid conductor 24. The present method ofreducing the diameter of a circular ferrule by first ovaling it and thenreforming it into a cylinder of circular cross section has been found tohave substantial advantages in making electrical-mechanical connectionsbetween a ferrule and a solid wire. In this embodiment, the conductor 24extends into the ferrule 28 and functions in the same manner as the plug12 of the embodiment of FIGURE 1.

While I have shown only preferred embodiments of my invention obviousmodifications thereof will be apparent to those skilled in the art. Forexample, it is contemplated that in some circumstances the bushing 12might be eliminated in the embodiment of FIGURE 1 particularly if thesheath 6 fits relatively closely over the insulated conductor 5. Undersuch circumstances of course, the sheath and the wire insulation whichare of plastic, rubber, or other elastic material, would function in thesame manner as the bushing functions in the embodiment of FIGURE 1 andwould be circumferentially compressed by the ferrule. It should also bementioned that seals in accordance with the invention are useful forhigh altitude (ie low ambient pressure) environments since at such lowpressures there is a greater tendency for corona discharges to takeplace than is the case under conditions of atmospheric pressure. Coronadischarges can be prevented under low pressure condi 'tions by sealingthe electrical connections in accordance with the invention.

I claim:

1. The method of compressing a ferrule of substantially circular crosssection onto a conductor extending therein comprising the steps of:forcing said ferrule into a female die having a width which is less thanthe di ameter of said ferrule and a depth which is greater than thediameter of the ferrule thereby partially to flatten said ferrule and toimpartto it a substantially oval-shaped cross section and to pinch saidconductor between the sides of said ferrule, and thereafter and whilesaid ferrule is retained in said female die, compressing said ferrule byapplication of a compressing force along the major axis of its ovalcross section to reduce said major axis until said ferrule is again ofsubstantially circular cross section and is in constrictive embracingrelationship with said conductor.

2. The method of forming a substantially impermeable seal between aninsulated conductor and a sleeve in surrounding relationship thereto andhaving a substantially circular ferrule thereon comprising the steps of:forcing said ferrule into a female die having a width less than thediameter of said ferrule thereby partially to flatten said ferrule andto impart to it a substantially ovalshaped cross section while pinchingsaid sleeve and said conductor along opposite sides, and thereaftercompressing said ferrule along its major axis to axially extrude saidferrule and to impart to itsferrule a substantially circular crosssection having a diametersubstantially equal to the Width of said dieand to compress said sleeve around said conductor.

References Cited in the file of this patent UNITED STATES PATENTS

